The invention relates to rolls for use in calenders and like machines wherein webs of paper, plastic or textile material are caused to advance through one or more nips each of which is defined by the peripheral surfaces of two neighboring rolls.
Commonly owned U.S. Pat. No. 4,757,584 granted Jul. 19, 1988 to Pav et al. for "Roll for use in calenders and the like" describes and shows a so-called controlled deflection roll wherein a deformable hollow cylindrical shell spacedly surrounds a non-rotatable carrier and can be deformed by one or more sets of deforming elements which are operated by pressurized hydraulic fluid and are surrounded by an elongated central portion of the shell. The set or sets of deforming elements are disposed between two antifriction bearings which surround the carrier and center the end portions of the shell. The axial ends of the shell cooperate with suitable seals to prevent penetration of air into, or to prevent escape of oil from, the interior of the shell. Furthermore, the shell confines two separating devices which are installed between the bearings and the adjacent deforming element or elements to ensure that a heated first liquid can be supplied to the deforming elements and that a preferably cooled or relatively cool second liquid can be fed to and can properly lubricate the bearings. The first liquid can also serve to operate and/or lubricate and/or otherwise beneficially influence one or more additional components or units of the patented roll. A heated first fluid is preferred in many instances in order to ensure that the peripheral surface of the roll is maintained at a requisite (often elevated) temperature for more satisfactory treatment of a running web of paper, plastic, textile material or the like. On the other hand, the temperature of the second liquid should not rise beyond a relatively low upper threshold value because the lubricating properties of a relatively cool second liquid (normally oil) are more satisfactory. The separating devices are supposed to establish barriers between a central zone or region within the shell which receives first liquid and two marginal or outer zones which contain the bearings and receive second liquid. Such rolls have been found to be highly satisfactory because the second liquid maintains the bearings in optimum condition while the first liquid can be used to operate the deforming elements as well as to heat the web-contacting portion of the roll to a desired elevated temperature. In other words, the first liquid cannot adversely influence (overheat) the second liquid, and the second liquid cannot adversely influence (cool) the first liquid. The disclosure of U.S. Pat. No. 4,757,584, together with that of each other U.S. patent referred to in the present specification, is incorporated herein by reference.
European patent application No. 0 179 730 of Allard for "Heated variable crown roll" (published Apr. 30, 1986) discloses a variable deflection or variable crown roll which is heatable and whose web-contacting peripheral surface is relatively short. The end portions of the shell are affixed to smaller-diameter sleeves which surround antifriction bearings mounted on the non-rotatable carrier of the roll. The roll further comprises annular chambers for a so-called insulating oil which is intended to prevent excessive transfer of heat between the lubricant for the bearings and the oil for the deforming means within the shell proper. It has been found that such design cannot invariably ensure adequate heating of the running web which is contacted by the peripheral surface of the roll.